Throughout the 90's, the number of battery-powered devices in the marketplace has grown in dramatic fashion. Dependence on these portable devices has transformed every aspect of our lives, from the critical tools of our professions, such as cellular phones and laptop computers, to the toys our children demand. This increase has fueled remarkable improvements in the design of battery-operated devices which differentiate products in vertical markets--and consume even more power than ever. This paradigm shift, which has taken portability from a novelty to a necessity, has led us to expect our tools to perform reliably and consistently. But even the best-designed portable products have an Achilles' Heel that has not been addressed. Batteries do not deliver the consistent reliability and performance that products require. They lose capacity, they deteriorate, and they allow our critical devices to fail us.
Rechargeable batteries have improved over the years as product designers have moved from nickel cadmium (NiCd) to nickel metal hydride (NiMH) to lithium ion (Li-Ion) to meet the increasing power demands. The nickel metal hydride battery is continually gaining popularity in the market and, up to this point, there has not been a satisfactory method of a terminating the charge cycle. The present termination methods, such as -.DELTA.V and maximum temperature (.DELTA.T/.DELTA.t), do not provide a satisfactory result, as batteries will heat up during charge and discharge because of the high level of hydrogen production in this chemistry.
For lead acid batteries the problems are worse. The basis of lead acid charging technology is 150 years old. Users of lead acid batteries experience a number of problems with battery corrosion, performance, and maintenance. Incorrect methods of charge and charge termination adversely affect the energy transformation properties and degrade the cycle life of the battery, thereby increasing the expense for battery maintenance. Currently, there are no accurate methods to determine when to terminate a charge cycle.
For lithium ion batteries, or modifications thereof, the existing, inaccurate methods of determining when to terminate or how to modify the energy transfer to the battery demand costly electronic circuitry inside the battery pack itself in order to prevent overcharging or overdischarging of the battery and to keep the battery operating in a safe temperature range.
Thus, battery reliability problems are still a top customer complaint throughout the portable industry. Newer battery chemistries cannot solve power problems when old charging and battery state monitoring routines are used. With all the effort spent developing new battery chemistries and improving old ones, little effort has been focused on the charging system. Without an effective charging system, a secondary battery is useless. With a standard charging system, a secondary battery is useful for powering a device, but lengthy charge times, capacity loss, and poor product performance are the norm. As long as batteries are a consumable product, and business projections depend on their obsolescence, battery manufacturers have no motivation to, and will not, build a better battery charger.
The following is a description of issued patents that individually offer only a partial solution to the many problems inherent in rechargeable batteries. U.S. Pat. Nos. 4,829,225 and 5,307,000 to Podrazhansky et al. are both prior patents issued to the inventor.
U.S. Pat. No. 4,829,225 to Podrazhansky et al. teaches a special technique for charging a battery with a single discharge pulse.
U.S. Pat. No. 5,307,000 to Podrazhansky et al. employs the use of multiple charge and discharge pulses to obtain an improved charging speed.
U.S. Pat. No. 3,816,807 to Taylor describes a technique for modulating a DC charging current with an AC voltage. The phase change of the modulating AC voltage is sensed with a phase detector and the change in phase is sent as a feedback signal to vary the DC power supply.
U.S. Pat. No. 5,329,219 to Garret describes a method and apparatus for charging a battery including a control circuit for determining the charge rate and charge capacity of a battery.
U.S. Pat. No. 5,331,268 to Pantino, et al. teaches a control for a trickle charge, which begins when a baseline voltage of the battery during a rapid charge attains a predetermined value.
U.S. Pat. No. 5,200,689 to Interiano et al. describes a battery charge controller and fuel gauge which continually monitors the voltage, temperature, and charge and discharge currents for a rechargeable battery, and calculates the battery's charge capacity and charge levels. The charge profile is similar to previously described techniques and is topped off with a trickle charge which will cause dendrite and other problems that are also applicable to the technique described in the '268 patent above.
U.S. Pat. No. 4,878,007 to Gabor et al. uses steep current pulses, superimposed on both charge and discharge pulses to produce a homogeneous electrode surface.
U.S. Pat. No. 4,746,852 to Martin teaches a controller for a battery charger that terminates battery charging operation as a function of a time derivative of the measured battery voltage.
U.S. Pat. No. 4,577,144 to Hodgman et al. describes a technique for distinguishing between primary and secondary batteries by sensing a charging or discharging parameter of a battery placed into the system. A ripple voltage is deemed to reflect the low frequency impedance of the AD battery during charging. A distinction between primary and secondary batteries is thus made as the low frequency impedance for a secondary battery is lower than that impedance for a primary battery of the same physical size.
U.S. Pat. No. 4,740,739 to Quammen et al. describes a battery charger and associated method for charging a DC battery utilizing a step-down transformer with high leakage reactance, and means for rectifying and regulating the step-down transformer output to continuously supply a constant charging current to the battery.
U.S. Pat. No. 3,987,353 to Macharg describes a technique for using charging pulses separated by intervals during which a change in the battery voltage is monitored and used to control the magnitude of the charging pulse.
U.S. Pat. No. 3,857,087 to Jones describes a method for testing lead acid batteries using both transient discharging and transient charging separated by a period of time to allow the battery to recover from either ion depletion or ion adsorption.